Sensitive and fast room temperature THz sensing: a challenge for Y-Ba-Cu-O semiconducting thin films

Abstract

The well known Y-Ba-Cu-O superconductor (oxygen rich) material also exhibits a semiconducting phase (oxygen depleted), which offers in its amorphous form (a-YBCO), an attractive solution for the easy fabrication of room temperature thermal radiation detectors. The operating mechanism is related to a sensitive pyroelectric response that originates from the permanent dipolar moment of the Y-Ba-Cu-O unit cell. In the first part of this paper, we investigate material aspects of a-YBCO thin films (surface morphology, electrical transport and optical properties) for a better understanding of the microstructure vs. conductivity relationship. In the second part, we report on the near-infrared (NIR) characterization of planar and trilayer detector devices fabricated on silicon substrates. These detectors exhibit a very fast response (time constant tau = 1.9 µs for a planar device; tau = 0.12 µs for a trilayer device) as compared to commercially available pyroelectric sensors. The best noise equivalent power (NEP) and detectivity D*, which are at the state of the art, were observed in the NIR at 10 kHz modulation frequency: NEP = 2.0 pW/rootHz and D* = 6.6×10^9 cm•rootHz/W for planar device; NEP = 2.6 pW/rootHz and D* = 5.7×10^9 cm•rootHz/W for trilayer device. Evolution towards THz detection is finally considered